Present-day concepts for industrial automation are based on the idea of decentralized controlling. The control task to be carried out is divided up among the control nodes of the decentralized control system in a geographically and functionally optimal manner. Thereby, the control nodes communicate with each other and with the superordinate systems via local networks. By means of the decentralized control, the time and effort involved in the communication process may be reduced as the individual control nodes autonomously take over control tasks relating to their respective areas and only have to communicate with the further control nodes and/or with the superordinate systems for coordination purposes.
In this context, the decentralized control is based on the idea of subdividing the automation task among individual functional and logically complete modules which may then be arranged in close proximity to the process, thus reducing the wiring and installation involved. By subdividing into modules, complexity may be reduced in order to enable a simpler functionality.
The Ethernet concept is the most widespread communication standard in local area networks. The Ethernet is based on a LAN configuration in which a plurality of control nodes, such as computers or machines, is connected to each other via a shared transmission medium, the Ethernet protocol carrying out the encapsulation of the data to be transmitted into data packets, in the following also referred to as telegrams, having a predetermined format.
Ethernet protocols are predominantly used for office communication networks. Due to the advantages of the Ethernet concept in using standard hardware and software components and due to the possibility of achieving high data transmission rates while utilizing a simple network technology, the Ethernet network communication is increasingly used in industrial manufacturing, as well, in order to exchange data between control nodes.
When controlling machines in industrial automation, it is required to cyclically process the control task without time fluctuations, i.e. with only little deviations from the desired cycle time in the range of a few microseconds, thereby reacting to the control demand with a foreseeable response time. Real-time functionality and fast response times as demanded in industrial automation, are, however, of only secondary significance in standard data processing applications for which the Ethernet communication is typically used. In order to guarantee real-time functionality and fast response times when using Ethernet communication in industrial automation, methods have been developed for prioritising Ethernet telegrams for real-time applications. Moreover, such modern data transmission processes frequently allow for the parallel use of the network for real-time and non-real-time applications, as well.
In spite of the increasing use of decentralized open control systems in which data transmission is carried out on the basis of the Ethernet protocol and the cost advantages resulting therefrom, a return-of-investment problem still exists in industrial automation, particularly due to increasingly shortening product cycles. Although new products are already developed in a way to allow for their simple automated production, the automation systems for manufacturing the products are usually specifically designed for the product to be manufactured and thus, adapting them to product and process modifications is only possible by means of a high amount of time and effort.